The present invention relates to a device for removing a deposit created in the electrolytic refining or electrowinning of metals from the surface of the mother plate used as an electrode in the refining or electrowinning process, when said removal is advantageously carried out without bending and hammering the mother plate.
When manufacturing many metals, such as copper, zinc or nickel, one of the major steps in the manufacturing process is electrolysis, where the metal to be produced is precipitated by means of an electric current conducted to the electrolyte on the surface of the electrode, i.e. the cathode. Normally the cathode is an object provided with a hanger for suspending the cathode in the electrolytic tank and connecting it to the circuit, as well as with a plate-like part to be immersed in the electrolyte, i.e. the mother plate, on the surface of which the metal to be produced is precipitated.
In modern production plants, the cathode plate is usually made of a different metal than the metal to be produced, and the two vertical edges of the cathode, or all three edges that are immersed in the electrolyte, are provided with electrical insulation, made for example of plastic, so that the metal precipitated on the surface of the cathode plate is divided in two separate plates at least on its two vertical sides. The production of permanent cathodes of the above described type, made of two different metals, is realised so that the metal to be produced is removed in plate-like sheets from the surfaces of the permanent cathodes, and the permanent cathodes are continuously circulated between the electrolytic tanks and the removal station. The electric insulation provided at the edges of the permanent cathodes is necessary particularly for removing and processing the precipitated metal.
The operation of the production process and the production of metal require that the metal to be produced is sufficiently often removed from the cathode plate surface. The interval between the removals is typically from one to seven days, and because the removal normally requires large-scale material transfers and an interruption in the process, the interval between removals is attempted to be made as long as possible. Therefore the metal deposits nowadays are usually fairly thick, generally well over 5 mm.
Because the plants producing copper, nickel and zinc are large in production quantities, said plants include thousands or tens of thousands of cathode plates, and even the number of cathode plates that daily enter removal is easily thousands or tens of thousands. Consequently, in order to remove the metal to be produced from the surfaces of permanent cathodes there are used mechanised and automated stripping machines. Moreover, because permanent cathodes are expensive in production costs, the maximisation of their working life is extremely important for the plant in question. It is true that the insulation provided at the cathode edges can be renewed, but it is advantageous for the plant to extend its lifetime, too. Thus among the most important features of a stripping machine is that the machine does not damage the permanent cathodes nor the permanent cathode edge insulation, that the produced metal is removed reliably and that the stripping machine is made to operate at a high speed.
Thus the object of the present invention is to realise an improved device for removing a deposit created in electrolytic refining or electrowinning from the surface of the mother plate used as an electrode, so that hard strains directed to the mother plate itself are avoided, such as bending or striking. The essential novel features of the invention are apparent from the appended claims.
According to the invention, in order to remove a metal deposit created in electrolytic refining or electrowinning, such as a copper, nickel or zinc deposit, from the surface of the mother plate of the electrode used in the electrolytic refining or electrowinning, there is employed a stripping machine that can be applied to removing the deposit essentially completely, or to removing the deposit only for an extent where a separate member can enter between the deposit and the mother plate in order to perform the final removal. The stripping machine according to the invention is provided with at least one gripping element, and by means of at least one control member connected to said gripping element, the gripping element is set to mechanical contact with the deposit to be removed from the mother plate. In order to position the gripping element essentially precisely with respect to the deposit, at least one of the gripping element control members is set to contact with the deposit, or at least with the surface that is clear of the metal deposit of the electrode. In connection with the removal operation proper, the gripping element of the stripping machine according to the invention is moved by means of a removal member proper, connected to the control member.
The stripping machine according to the invention is supported against a frame structure that simultaneously constitutes a removal station for the deposit created on the mother plate in the electrolytic refining or electrowinning process. Normally the deposit in electrolytic refining or electrowinning is created on two opposite sides of the mother plate, and therefore there are at least two removal members arranged in the removal station, advantageously so that for each deposit, there is provided at least one device on both sides of the mother plate. If a separate device is used for removing the deposit after a preliminary removal carried out by a stripping machine according to the invention, said separate device being for instance a knife, said removal knife can also be installed in the same removal station. The removal knife can also be located as separate from the removal station formed by the stripping machine.
When using a stripping machine according to the invention, the mother plate that is circulated between the electrolytic refining or electrowinning process and the removal station, and which in that case is a permanent cathode, does neither have to be bent nor otherwise strained, which is advantageous for the working life of the permanent cathode. Moreover, owing to the control member provided in the stripping machine, the gripping element is not in contact with the surface of the mother plate, i.e. of the permanent cathode. Further, neither the control member nor any other part of the stripping machine is in contact with those parts of the permanent cathode that in electrolytic refining or electrowinning go underneath the electrolyte surface, in which case the part of the permanent cathode that is active in creating the deposit is made to remain essentially unbroken and advantageous for the creation of the deposit. The advantageous nature of the stripping machine according to the invention is enhanced by the fact that the motions directed to the control members and to the gripping element are essentially short, and thus the removal operation proper can be carried out rapidly.
When using the stripping machine according to the invention, the mother plate serving as the permanent cathode does not have to be bentxe2x80x94said mother plate usually being provided with edge strips in order to prevent the deposit from growing over the mother plate edgesxe2x80x94and hence the working life of the mother plate edge strips can be also extended, because bending would possibly cause cracks in the edge strips, which would make said edge strips unusable. Furthermore, when using the stripping machine according to the invention, the removal of particularly thick deposits is carried out reliably, because with thick deposits the required bending forces would be the stronger, the thicker the deposits are.
When the permanent cathode, complete with metal deposits, is attached to the removal station in the beginning of the removal operation, the stripping machine according to the invention is shifted to removal position by utilising the elements connected to the control member of the gripping element, i.e. the gripping element shaft part and the stripping machine proper. The gripping element shaft part is installed movably, so that the control member and consequently also the gripping element can be moved essentially in the direction of the mother plate surface. On the other hand, the stripping machine proper is installed movably, so that the stripping machine can be moved in a direction essentially perpendicular to the mother plate surface. Moreover, the gripping element shaft part is installed so that the shaft part can be rotated around its axis. Owing to these separate motions, the gripping element can be set to a position that is advantageous for the removal with respect to the metal deposit.
In the device according to the invention, the moving of the gripping element and simultaneously the moving of the control member either in an essentially parallel direction with the mother plate surface, or in an essentially perpendicular direction to the mother plate, can advantageously be carried out either hydraulically, pneumatically or electrically. Similar methods can also be applied when rotating the gripping element shaft part around its axis.